1. Field of the Invention
The present invention relates to a polysilicon thin film and a method of preparing the same.
2. Description of the Background Art
A polysilicon thin film is employed as a photoelectric conversion layer in a photovoltaic element or the like. It is necessary to improve the photoelectric conversion efficiency in such a photovoltaic element. Thus, it is necessary to increase the sizes of the crystal grains forming the polysilicon thin film for improving the carrier mobility and increasing the carrier diffusion length in the thin film as a means for improving the photoelectric conversion efficiency.
The so-called solid phase growth method of forming an amorphous silicon thin film on a substrate and crystallizing the amorphous silicon thin film by heat treating the same is known as an exemplary method of preparing a polysilicon thin film. Further, the so-called partial doping method is known as a method of preparing a polysilicon thin film having large crystal grain sizes by the solid phase growth method. The partial doping method is adapted to partially dope an amorphous silicon thin film with phosphorus (P) or boron (B) thereby changing the conductivity type or charge carrier type of the amorphous silicon film and selectively starting crystallization from the doped part. According to the partial doping method, crystallization is started from a specific part of the amorphous silicon thin film, whereby it is possible to control the generation of crystal nuclei for obtaining a polysilicon thin film having relatively large crystal grain sizes.
However, such a polysilicon thin film obtained by the conventional partial doping method is limited as to further improvement of the photoelectric conversion efficiency of a photovoltaic element.